protoc plugin for JSON converter

These protoc plugins use a simple JSON encoding.

An instance of the following protobuf:

message Foo {
  message Bar {
    repeated string rabbits = 1;
  }
  optional string cat = 1;
  repeated int32 dog = 2;
  optional Bar rabbit_den = 3;
}

could be encoded to something like:

{
  "1": "kitty",
  "2": [4, 16, 9],
  "3": { "1": ["thumper", "oreo", "daisy"] }
}

Only a limited part of the protocol buffer IDL is supported.

• Supported field types: float, double, int32, bool, string, message, and enum

• Supported field rules: optional, repeated

• Unsupported features:

  • default values
  • imports
  • extensions
  • services
  • non-file-level options